In internal combustion engines, vibrations are transmitted from the engine block to other engine parts, such as the oil pan and transmission cover as well as to the car body through engine mounts. Also airborne noise is generated in the engine, e.g. in engine covers. This is especially a problem in diesel engines, where the engine noise known as “diesel knocking” is expected to increase with the introduction of new emission regulations, the required increased combustion pressure resulting in increased levels of high-frequency engine-block vibrations.
There is also a tendency in the automotive industry to attempt to reduce the weight of the vehicles by producing automotive parts, such as engine parts, with thinner walls and/or in more light-weight materials, which are more susceptible to vibrations. The problems of undesired vibrations and noise are therefore increasing.
Various attempts to counteract vibrations in internal combustion engines have been described in the prior art.
EP 1 956 223 A1 discloses an internal combustion engine block assembly having a cylinder case placed above an oil pan, where a vibration-damping plate is interposed between the case and the pan and fixed, in its periphery, to the case and the pan. The plate is constituted of an elastomeric central core placed between a lower metal sheet and an upper metal sheet, each of 50 times higher stiffness than that of the elastomeric core. To permit crankshaft motion, openings are provided in the plate delimiting connecting members which extend across the oil pan enclosure.
In one embodiment, the two metal sheets have a groove along the longitudinal axis of the sheet on one side of the connecting members, opposite to that of the other sheet. This reduces the rigidity of the sheets sufficiently to permit the sandwich plate to elongate and contract through shear of the core layer, thereby damping certain modes of vibrations. In use such vibration-damping plates have lead to oil leakage between the engine block and oil pan.
An analogous approach has been described in Wiman, U., Automotive Engineering 16 (2008):10, p. 34, 36, “Shear plate reduces diesel engine noise”. A sandwich “shear plate” consisting of a middle rubber layer vulcanized together with two steel layers, is positioned between the engine block and the oil pan below the crankshaft in an internal combustion engine. The shear plate has milled grooves in the steel layers held together by the middle rubber layer. The upper steel layer is fastened to one side of the engine block, and the lower layer is fastened to the other. Thereby, shearing, and thus damping, is produced in the middle layer.
JP-07-317600 discloses a noise-reducing structure for an oil pan constituted by a stiffening plate secured to the side walls of the oil pan at a position near the oil pan mounting surface to the engine block. Thereby, the vibration amplitudes of the oil pan side walls during piston motion are reduced and noise generation is suppressed.
FR 2849467 A1 discloses an internal combustion engine having an anti-emulsion plate of rigid solid material, such as high gauge metal, for stiffening the walls of the oil pan. The plate is fixed inside the pan dividing it into an upper chamber and a lower oil reservoir. A further stiffening plate in the form of a windage tray is fixed below the peripheral edge of the cylinder block skirt in such a way that it extends between the walls of the oil pan without being pinched between the bottom peripheral edge of the cylinder block and the top edge of the oil pan. Thereby sealing between the oil pan and the engine block can be ensured by other means.
U.S. Pat. No. 6,621,658 B1 discloses a vibration damping structure, particularly a cover for a disk drive assembly, comprising two metal skins and a damping layer in the form of a viscoelastic material capable of adhering to the metal skins. At a fastener location of the cover, an aperture for a screw is provided through the structure, and each of the metal skins has a single linear cut therein which is circular and coaxial with the aperture, the cut in one metal skin being of a different diameter than the cut in the other metal skin. The cuts prevent mechanical vibrations transmitted via the screw to the area immediately surrounding the aperture from propagating into the rest of the structure.
It is an object of the present invention to provide improved vibration damping of hollow bodies and vibration-prone surfaces, especially in automotive enclosure articles, such as oil pans, valve covers, gear box covers, transmission covers etc.